Sealing device and a method of repairing/replacing sealing devices

ABSTRACT

A sealing device (20, 80, 90), optionally in the form of a kit is provided for sealing about a rotatable member such as a shaft (22). The sealing device or the kit includes a follower housing (32) for mounting about the rotatable member (32) with an axial direction of the follower housing aligned with the rotational axis of the rotating member. Further, a follower (40, 40 a , 40 b ) is provided for compressing a primary seal, such as packing (28), for sealing against the rotatable member. The follower is slidable within the follower housing generally in the axial direction and has sliding interfaces for interfacing with the follower housing and/or the rotatable member. There is also a chamber (68, 108) or simply a recess defined by the housing and a pressure face of the follower, with the chamber/recess being configured to receive fluid. A secondary seal (58) is also provided at the sliding interfaces for sealing against the egress of fluid in use, from the chamber/recess along the sliding interfaces of the follower.

FIELD OF THE INVENTION

The present invention relates to sealing devices. In particular,although not exclusively, the invention relates to a gland wherein fluidpressure is applied to energise the follower. The invention also relatesto repair and replacement of conventional sealing devices.

BACKGROUND TO THE INVENTION

A conventional shaft sealing arrangement is illustrated in FIG. 1 andindicated by numeral 10. The shaft sealing arrangement 10 is arranged toprovide a fluid seal around the shaft 11 where the shaft 11 exists themachine housing through a portion of the machine housing 12. The portion12 defines an annular recess adjacent the shaft 11 in which packing 14is provided. A gland follower 16 operates to compress the packing 14within the recess. As the packing 14 is compressed axially ie parallelto the axis of the shaft 11, the packing 14 applies a radial force tothe shaft 11, thereby sealing against the shaft. The gland follower 16is secured to the portion 12 of the machine housing by bolts 18 and nuts20. The nuts and bolts 18, 20 can also control the compressive forceapplied by the gland follower 16 to the packing 14. As shown, the shaftsealing arrangement 10 is conventionally assembled between the portion12 of the machine housing and the bearing 13. The bearing 13 is retainedin place by bearing bracket 15 secured by fasteners 17.

A disadvantage of this arrangement is that as the packing 14 wears thecompressive force applied to the packing 14 will decrease. Therefore,regular maintenance checks are required. This may involve regulartightening of the nuts 20. The labour involved in maintainingconventional sealing arrangements 10 in operating order is thereforehigh.

The illustrated arrangement in FIG. 1 shows considerable space betweenthe machine housing 12 and the bearing 13. This is not always the caseand where the portion 12 is closely spaced to the bearing 13,difficulties will be encountered in accessing and tightening nuts 20.Further difficulties will also be encountered in repacking the packing14 as required.

It is therefore an object of the present invention to provide a sealingdevice which overcomes or at least ameliorates some of the abovementioned disadvantages. Additionally, it is an aim of a preferredembodiment of the present invention to replace of the present inventionis at least to provide the public with a useful choice.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided asealing device for sealing about a rotatable member extending through amachine housing, the sealing device including: primary sealing meansdisposed in a recess of the machine housing for sealing against therotatable member; a follower for compressing the primary sealing means;a follower housing connected to the machine housing and of annular formfor mounting about the rotatable member with an axial direction of thefollower housing aligned with the rotational axis of the rotatablemember, wherein the follower housing includes inner and outer annularwalls, with the follower having an annular body portion which isslidingly engageable with both the inner and outer annular walls, anannular chamber being defined by the inner and outer annular walls and apressure face of the follower, the chamber having means to receivefluid; the follower being slidable within the follower housing generallyin the axial direction and having sliding interfaces for interfacingwith the inner and outer walls of the follower housing, there beingfurther provided, secondary sealing means at the sliding interfaces forsealing against the egress of fluid from the chamber along the slidinginterfaces of the follower.

The sealing device defined above may be used in any application where aconventional sealing device is used eg. pumps, augers, valves.

The primary sealing means may be in the form of packing conventionallyused in sealing devices although other sealing means such as elastomericrings are considered within the scope of the present invention.

Preferably the follower is in the form of an annular piston receivedwithin the follower housing. In a preferred form of the invention, thepiston further includes an annular extension extending beyond thefollower housing and into the recess in the machine housing. Thefollower may come in two or more parts such as two symmetrical halves toaid assembly.

The follower housing may come in two or more parts such as twosymmetrical halves to aid assembly.

The secondary sealing means may be of any form although conventionalpiston rings are the preferred form.

The sealing device may be adapted to utilise any fluid such as air orhydraulic fluid for energising the follower. When the sealing device isused in applications transferring a clean liquid eg. water, oil orstream, a connection may be provided from the discharge of thetransferring apparatus to the sealing device. In other applications, anindependent fluid supply may be adopted. This might include a source ofcompressed air or a hydraulic system could be employed.

Additionally, control means may be provided to control the fluidpressure. Preferably the control means provides a constant fluidpressure to the chamber. Thus if the chamber starts to leak, furtherfluid will be provided to maintain the pressure and the sealing deviceremains in operation. The control system may be adapted to provide analarm condition when the amount of further fluid reaches an unacceptablelevel. The control system may comprise a P.L.C. with feedback.Alternatively, an air cylinder with a regulator may be appropriate.

In another preferred form of the invention, the follower may comprisetwo parts, a first packing portion and a second piston portion. Thefirst packing portion maybe in the form of an annular body portion withan annular extension. The second piston portion may be in the form of anannular piston. The two portions may be held in spaced configuration bya biasing means urging the two portions apart, such as a spring.Moreover, instead of an open fluid system whereby the chamber issupplied with fluid to a predetermined pressure, the fluid system may beessentially closed. For example, the follower housing may define aforward chamber between the first follower portion and the forward wallof the housing and a rear chamber between the second piston portion andthe rear wall of the follower housing. The forward and rear chambers areinterconnected for fluid flow therebetween. Furthermore, the pressureface of the first follower portion against which the fluid acts in usemay be smaller than the pressure face of the second portion to maintaina greater force against the second portion than the first portion, thisdifference being balanced by the reaction force acting against the firstfollower by the packing. As the packing wears with a consequentreduction in the reaction force applied to the first follower portion,the greater force on the second follower portion urges both followerportions forwardly, with the force being transmitted through the springto the first follower portion. This brings about a consequent reductionin the volume of the forward chamber. With the first and second chambersfluid-filled in use, a reduction in the volume of the forward chamberwill cause fluid to flow to the second chamber. As the area of thepressure face of the second follower portion is greater than the first,the second follower portion will not move the same distance as the firstfollower portion. The spring thus takes up the slack between the twofollower portions.

It will be appreciated that the various parts are unlikely to move instep-wise fashion as explained above. Rather, it is expected that thevarious parts of the device move gradually to retain equilibrium of thevarious forces acting on the various parts.

In accordance with a second aspect of the present invention, there isprovided a kit for sealing about a rotatable member extending through amachine housing, the kit including: a follower for compressing packingwhich is disposed within a recess of the machine housing against therotatable member; a follower housing connectable to the machine housingand of annular form for mounting about the rotatable member with anaxial direction of the follower housing aligned with the rotational axisof the rotatable member, wherein the follower housing includes inner andouter annular walls, with the follower having an annular body portionwhich is slidingly engageable with both the inner and outer annularwalls, an annular chamber being defined by the inner and outer annularwalls and a pressure face of the follower, the chamber having means toreceive fluid; the follower being slidable within the follower housinggenerally in the axial direction and having sliding interfaces forinterfacing with the inner and outer walls of the follower housing,there being further provided, secondary sealing means at the slidinginterfaces for sealing against the egress of fluid from the chamberalong the sliding interfaces of the follower.

The preferred features recited above in connection with the first aspectof the invention may also have application in respect of the secondaspect of the invention, including the feature of the two part follower.

The kit may be retro-fitted onto a rotatable member with a conventionalsealing device. In so doing, the packing may be repacked. Preferably,the installation is achieved by removing the existing gland follower andnut of the conventional sealing device and replacing this with the kitas defined. The follower housing may be attached to the machine housingto which the gland follower was previously attached. This may beachieved by providing a portion of the follower housing as an attachmentplate which is initially attached to the machine housing. The remainingportion of the follower housing is connectable to the attachment platewith the follower positioned to act against the packing.

In certain applications, there may be insufficient clearance between themachine housing and an adjacent bearing bracket to insert the followerhousing and follower. In such cases, the kit may be installed byattaching the follower housing to the bearing bracket. An adaptor meansmay be provided for this purpose.

The secondary sealing means may be in any form although conventionalpiston rings are the most preferred.

The kit may also include means for applying fluid to the chamber.

In accordance with a third aspect of the present invention, there isprovided a method of upgrading a conventional sealing device for arotatable member extending through a machine housing where theconventional sealing device includes a gland follower attached to themachine housing and packing disposed in a recess of the machine housingagainst the rotatable member, the method including: removing the glandfollower of the conventional sealing device; and installing a kitcomprised of a follower and follower housing by attaching the followerhousing to the machine housing, with the follower positioned to actagainst the packing, wherein the follower housing is of annular form formounting about the rotatable member with an axial direction of thefollower housing aligned with the rotational axis of the rotatablemember, wherein the follower housing includes inner and outer annularwalls, with the follower having an annular body portion which isslidingly engageable with the inner and outer annular walls, an annularchamber being defined by the inner and outer annular walls and apressure face of the follower, the chamber having means to receivefluid, the follower being slidable within the follower housing generallyin the axial direction and having sliding interfaces for interfacingwith the inner and outer walls of the follower housing, there beingfurther provided, secondary sealing means at the sliding interfaces forsealing against the egress of fluid from the chamber along the slidinginterfaces of the follower.

Preferably the follower housing is installed by the use of an attachmentplate forming part of the follower housing. The attachment plate may beconnected in place of the existing gland follower(s). Optionally thesame fastening means may be used. The remaining part of the housing maythen be secured to the attachment plate. A threaded connection betweenthe remaining part of the housing and the attachment plate may beprovided for this purpose.

It will be appreciated that the use of the follower housing may take upadditional space when compared with the existing sealing arrangement. Insome applications therefore, there may be insufficient room between themachine housing and the bearing bracket for the replacement follower andfollower housing to be installed given the required configuration of thereplacement follower. In such applications, the follower housing may besecured to the bearing bracket by the use of an adaptor means.

In accordance with a fourth aspect of the present invention, there isprovided a method of upgrading a conventional sealing device for arotatable member extending through a machine housing where theconventional sealing device includes a gland follower attached to themachine housing and packing disposed in a recess of the machine housingagainst the rotatable member, with a bearing bracket positioned adjacentthe machine housing, the method including; removing the gland followerof the conventional sealing device; and installing a kit comprised of afollower and follower housing by attaching the follower housing to thebearing bracket, with the follower positioned to act against thepacking, wherein the follower housing is of annular form for mountingabout the rotatable member with an axial direction of the followerhousing aligned with the rotational axis of the rotatable member,wherein the follower housing includes inner and outer annular walls,with the follower having an annular body portion which is slidinglyengageable with the inner and outer annular walls, an annular chamberbeing defined by the inner and outer annular walls and a pressure faceof the follower, the chamber having means to receive fluid, the followerbeing slidable within the follower housing generally in the axialdirection and having sliding interfaces for interfacing with the innerand outer walls of the follower housing, there being further provided,secondary sealing means at the sliding interfaces for sealing againstthe egress of fluid from the chamber along the sliding interfaces of thefollower.

Either of the above methods may additionally include repacking thepacking.

The replacement follower may take any of the forms described above inconnection with the first aspect of the invention including the two partform.

This invention may also be said broadly to consist in the parts,elements and features referred to or indicated in the specification ofthe application, individually or collectively, and any or allcombinations of any two or more said parts, elements or features, andwhere specific integers are mentioned herein which have knownequivalents in the art to which this invention relates, such knownequivalents are deemed to be incorporated herein as if individually setforth.

The invention consists in the foregoing and also envisages constructionsof which the following gives examples only.

BRIEF SUMMARY OF THE DRAWINGS

In order that the invention may be more full understood, someembodiments will now be described by way of example with reference tothe drawings in which:

FIG. 1 is a sectional view of a conventional sealing device mounted on ashaft forming part of a machine;

FIG. 2 is a part sectional view of a sealing device in accordance with apreferred embodiment of the present invention;

FIG. 3 is a perspective view, partially cut away, of the sealing deviceillustrated in FIG. 2;

FIG. 4 is a sectional view of a sealing device in accordance with asecond preferred embodiment of the present invention;

FIG. 5 is a sectional view of a sealing device in accordance with athird preferred embodiment of the present invention; and

FIG. 6 is a sectional view of a sealing device in accordance with afourth aspect of the present invention.

PREFERRED MODES OF CARRYING OUT THE INVENTION

As illustrated in FIG. 2, the sealing device or gland 20 is assembledabout a shaft 22. The assembly also includes a portion of the machinehousing 24. The portion of the machine housing 24 is annular in form andextends about the shaft 22. As in the conventional sealing arrangement,the portion of the machine housing 24 includes an annular recess 26which extends adjacent the shaft 22 for a small portion of the length ofthe shaft. The annular recess 26 receives primary sealing means 28 whichmay be in the form of conventional packing. The packing 28 abuts againstan internal annular shoulder 30 defining part of the annular recess 26.The annular shoulder 30 constrains movement of the packing 28 along theshaft 22 in the leftward direction from the point of view shown in FIG.2.

A follower housing 32 is attached to the portion of the machine housing24. As can be seen more clearly in FIG. 3, the follower housing 32comprises an attachment plate 34 and a remaining portion in the form ofan annular cylinder 36. The follower housing 32 is attached to theportion 24 of the machine housing by means of the attachment plate 34. Athreaded connection is provided between the annular cylinder 36 and theattachment plate 34 to facilitate assembly of the follower housing 32.

Received in the follower housing 32 is a follower 40. As illustrated,the follower 40 has a first annular body portion 44 and a second annularextension portion 46. The body portion 44 is slidable within the annularcylinder 36 between opposing annular inner wall 48 and annular outerwall 50. The body portion 44 of the follower 40 has inner and outersliding interfaces 54, 56 making sliding contact with the inner wall 48and the outer wall 50 respectively. Secondary sealing means in the formof piston rings 58 are provided at the inner and outer interfaces 54,56. and outer walls 48, 50 of the cylinder 36 and a pressure face 62 ofthe follower 40. The pressure face 62 is opposite the end wall of thecylinder 36.

The chamber 68 includes an inlet 70 for supply of compressed air.Preferably, a constant pneumatic pressure is applied to the chamber 68,acting against pressure face 62 of the follower 40.

The annular extension portion 46 extends through an annular gap providedbetween the attachment plate 34 and the shaft 22 to bear against thepacking 28. It will be understood that with a constant pressure appliedto the chamber 68, the follower 40 will be urged in the axial directiontoward the packing 28. The extension portion 46 of the follower 40 willpush axially against the packing 28 which is constrained from furthermovement by the annular shoulder 30. The resultant compression of thepacking 28 applies a radial force to the shaft 22 to provide a sealabout the shaft 22.

FIG. 4 illustrates a second preferred embodiment of a sealing device orgland 80 which is similar in many respects to the first embodiment ofthe sealing device 20 illustrated in FIGS. 2. Like numerals representlike parts. The sealing device 80 may be installed in place of theconventional sealing device 10 illustrated in FIG. 1. The sealing device10 may be repaired or substantially replaced by removing the nuts 20 torelease the tension in bolts 18 and to enable the gland follower 16 tobe removed from the position illustrated. The gland follower 16 issuitably in two parts to aid in its assembly and effect removal. Withthe gland follower removed, the packing 14 may be repacked.

The conventional sealing device 10 is replaced by the sealing device orgland 80. As an initial step the attachment plate 34 is secured to theportion of the machine housing 12 through the use of the existing boltholes. As shown, a threaded connection is provided between theattachment plate 34 and the cylinder 36. The follower housing 32 isthereby assembled in place with the replacement follower 40 operable tocompress the packing 14. The air supply is then provided to the followerhousing 32, in a similar manner to that illustrated in FIG. 2, althoughthis is not illustrated in FIG. 4.

In the alternative embodiment illustrated in FIG. 5, the attachmentplate 34 is dispensed with. Instead, an adapter means is used to connectthe sealing device or gland 90 to the bearing bracket. An adapted plate92 is secured to the end wall of the annular cylinder 36. this adapterplate 92 is then secured by means of connectors 94 and connector plate96 40 to receive pressurised air to force the follower 40 to compressthe packing 14.

In the fourth embodiment illustrated in FIG. 6, the follower housing isdefined in part by the machine housing 24 and an attachment portion 36a. The attachment portion 36 a is externally threaded and the machinehousing 24 is internally threaded for engagement will the internalthread of the attachment portion 36 a. Inside the follower housing, thefollower may comprise two parts, a first packing portion 40 a and asecond piston portion 40 b. The first packing portion 40 a may be in theform of an annular body portion 100 with an annular extension 102. Thesecond piston portion 40 b may be in the form of an annular piston. Thetwo portions 40 a, 40 b may be held in a spaced configuration by aspring 104 biasing the two portions apart. The follower housing includesa forward chamber 106 between the first follower portion 40 a and theforward wall of the machine housing 24 and a rear chamber 108 betweenthe second piston portion 40 b and the rear wall of the attachmentportion 36 a. The forward and rear chambers 106, 108 are interconnectedby a passage 110 having a check valve 112.

The first and second chambers 106, 108 are oil-filled in use to apredetermined pressure. The filling may be achieved through port 114.The pressure face of the first follower portion 40 a against which thefluid acts is smaller than the pressure face of the second portion 40 bto maintain a greater force against the second portion 40 b than thefirst portion 40 a, this difference being balanced by the reaction forceacting against the first follower 40 a by the packing 30. As the packing30 wears with a consequent reduction in the reaction force applied tothe first follower portion 40 a, the greater force on the secondfollower portion 40 b urges both follower portions 40 a, 40 b forwardly,with the force being transmitted through the spring 104 to the firstfollower portion 40 a. This brings about a consequent reduction in thevolume of the forward chamber 106. With the first and second chambers106,108 fluid-filled in use, a reduction in the volume of the forwardchamber 106 will cause fluid to flow to the second chamber 108 alongpassage 110 through check valve 112. As the area of the pressure face ofthe second follower portion 40 b is greater than the first 40 a, thesecond follower portion 40 b will not move the same distance as thefirst follower portion 40 a. The spring 104 thus takes up the slackbetween the two follower portions 40 a, 40 b.

It will be appreciated that the various parts are unlikely to move instep-wise fashion as explained above. Rather, it is expected that thevarious parts of the device move gradually

It will be understood that the above described only some embodiments ofthe present invention and modifications may be made thereto withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A kit for sealing about a rotatable memberextending through a machine housing, the kit including: a followerhousing connectable to the machine housing and of annular form formounting about the rotatable member with an axial direction of thefollower housing aligned with the rotational axis of the rotatablemember, wherein the follower housing includes spaced apart inner andouter annular walls encircling the rotatable member; a follower forcompressing packing which is disposed within a recess of the machinehousing against the rotatable member, the follower having an annularbody portion slidingly engageable with both the inner and outer annularwalls of the follower housing, the follower being slidable within thefollower housing generally in the axial direction and having slidinginterfaces for interfacing with the inner and outer annular walls of thefollower housing; an annular chamber encircling the rotatable member,the annular chamber being at least partially defined by the inner andouter annular walls of the follower housing and an annular pressure faceof the follower, the chamber having means for receiving fluid; andsecondary sealing means at the sliding interfaces for sealing againstthe egress of fluid from the chamber along the sliding interfaces of thefollower.
 2. The kit as claimed in claim 1 installed to connect to themachine housing.
 3. The kit as claimed in claim 1 wherein the followerfurther includes an annular extension bearing against the packing. 4.The kit as claimed in claim 1 wherein the secondary sealing means are inthe form of piston rings incorporated into the follower.
 5. The kit asclaimed in claim 1 including a source of fluid.
 6. The kit as claimed inclaim 5 further including control means adapted in use to allow theentry of additional fluid from the source to the chamber duringoperation to maintain a constant fluid pressure in the chamber.
 7. Thekit as claimed in claim 6 wherein the control system is adapted toprovide an alarm condition when the rate of entry of additional fluidexceeds a predetermined threshold.
 8. The kit as claimed in claim 5wherein the source of fluid is an air cylinder and a regulator.
 9. Thekit as claimed in claim 1 wherein the follower comprises: a firstfollower portion adapted to act against the packing, and a secondfollower portion, the two portions being held in spaced configuration bya biasing means urging the two portions apart.
 10. The kit as claimed inclaim 9 wherein there is provided: a forward fluid chamber between apressure face of the first follower portion and a forward wall of thehousing; a rear fluid chamber between a pressure face of the secondfollower portion and a rear wall of the follower housing; the forwardand rearward chambers being interconnected for fluid flow therebetweenand adapted to operate as a closed system in normal use, wherein thepressure face of the first follower portion is smaller than the pressureface of the second portion.
 11. The kit as claimed in claim 10 wherein:the first follower portion is in the form of an annular body portionwith an annular extension adapted to act against the primary sealingmeans, and the second follower portion is in the form of an annularpiston.
 12. The kit as claimed in claim 9 wherein the biasing means is aspring.
 13. The kit as claimed in claim 1 wherein the follower housingincludes an attachment to secure the follower housing to the machinehousing.
 14. The kit as claimed in claim 1 further comprising anattachment to secure the follower housing to a bearing bracket adjacentthe machine housing.
 15. A method of installing the kit as claimed inclaim 1 by retro-fitting the kit about a rotatable member previouslyfitted with a conventional sealing device.
 16. A method of upgrading aconventional sealing device for a rotatable member extending through amachine housing where the conventional sealing device includes a glandfollower attached to the machine housing and packing disposed in arecess of the machine housing against the rotatable member, the methodcomprising: removing the gland follower of the conventionally sealingdevice; and installing a kit comprised of a follower and followerhousing by attaching the follower housing to the machine housing, withthe follower positioned to act against the packing, wherein the followerhousing is of annular form for mounting about the rotatable member withan axial direction of the follower housing aligned wit the rotationalaxis of the rotatable member, wherein the follower housing includesspaced apart inner and outer annular walls encircling the rotatablemember, with the follower having an annular body portion slidinglyengageable with both the inner and outer annular walls of the followerhousing, an annular chamber encircling the rotatble member, the annularchamber being at lest partially defined by the inner and outer annularwalls of the follower housing and an annular pressure face of thefollower, the chamber having means for receiving fluid, the followerbeing slidable within the follower housing generally in the axialdirection and having sliding interfaces for interfacing with the innerand outer annular walls of the follower housing, there being furtherprovided, secondary sealing means at the sliding interfaces for sealingagainst the egress of fluid from the chamber along the slidinginterfaces of the follower.
 17. A method of upgrading a conventionalsealing device for a rotatable member extending through a machinehousing where the conventional sealing device includes a gland followerattached to the machine housing and packing disposed in a recess of themachine housing against the rotatble member, with a bearing bracketpositioned adjacent the machine housing, the method comprising: removingthe gland follower of the conventional sealing device; and installing akit comprised of a follower and follower housing by attaching thefollower housing to the bearing bracket, with the follower positioned toact against the packing, wherein the follower housing is of annular formfor mounting about the rotatable member with an axial direction of thefollower housing aligned with the rotational axis of the rotatablemember, wherein the follower housing includes spaced apart inner andouter annular walls encircling the rotatble member, with the followerhaving an annular body portion slidingly engageable with both the innerand outer annular walls of the follower housing, an annular chamberencircling the rotatable member, the annular chamber being at leastpartially defined by the inner and outer annular walls of the followedhousing and an annular pressure face of the follower, the chamber havingmeans for receiving fluid, the follower being slidable within thefollower housing generally in the axial direction and having slidinginterfaces for interfacing with the inner and outer annular walls of thefollower housing, there being further provided, secondary sealing meansat the sliding interfaces for sealing against the egress of fluid fromthe chamber along the sliding interfaces of the follower.
 18. The methodas claimed in claim 16 wherein the follower housing is installed by theuse of an attachment plate forming part of the follower housing, theattachment plate being connected in place of the gland follower(s) withthe remaining part of the housing being subsequently secured to theattachment plate.
 19. The method as claimed in claim 17 wherein thefollower housing is secured to the bearing bracket by the use of anadaptor device.
 20. The method as claimed in claim 16 wherein anindependent fluid supply is connected to the chamber.
 21. A sealingdevice for sealing about a rotatable member extending through a machinehousing, the sealing device comprising: primary sealing means disposedin a recess of the machine housing for sealing against the rotatablemember; a follower for compressing the primary sealing means; a followerhousing connected to the machine housing and of annular form formounting about the rotatable member with an axial direction of thefollower housing aligned with the rotational axis of the rotatablemember, wherein the follower housing includes spaced apart inner andouter annular walls encircling the rotatable member, with the followerhaving an annular body portion slidingly engageable with both the innerand outer annular walls of the follower housing, an annular chamberencircling the rotatable member, the annular chamber being at leastpartially defined by the inner and outer annular walls of the followerhousing and an annular pressure face of the follower, the chamber havingmeans for receiving fluid; and the follower being slidable within thefollower housing generally in the axial direction and having slidinginterfaces for interfacing with the inner and outer annular walls of thefollower housing, there being further provided, secondary sealing meansat the sliding interfaces for sealing against the egress of fluid fromthe chamber along the sliding interfaces of the follower.
 22. Thesealing device as claimed in claim 21 wherein the follower is in theform of an annular piston.
 23. The sealing device as claimed in claim 22wherein the piston has an annular body portion received in the followerhousing and an annular extension.
 24. The sealing device as claimed inclaim 21 wherein the secondary sealing means are in the form of pistonrings incorporated into the follower.
 25. The sealing device as claimedin claim 21 wherein the sealing device is adapted to operate as an opensystem whereby the chamber receives fluid from a source external to thesealing device.
 26. The sealing device as claimed in claim 25 whereinthe sealing device is adapted to receive air from a source of compressedair.
 27. The sealing device as claimed in claim 25 further comprisingcontrol means adapted in use to allow the entry of additionally fluidfrom the source to the chamber to maintain a constant fluid pressure inthe chamber.
 28. The sealing device as claimed in claim 27 wherein thecontrol system is adapted to provide an alarm condition when the rate ofentry of additional fluid exceeds a predetermined threshold.
 29. Thesealing device as claimed in claim 21 wherein the follower comprises: afirst follower portion adapted to act against the primary sealing means;and a second follower portion, the two portions being held in spacedconfiguration by a biasing means urging the two portions apart.
 30. Thesealing device as claimed in claim 29 wherein there is provided: aforward fluid chamber between a pressure face of the first followerportion and a forward wall of the housing; a rear fluid chamber betweena pressure face of the second piston portion and a rear wall of thefollower housing; the forward and rearward chambers being interconnectedfor fluid flow therebetween and adapted to operate as a closed system innormal use, wherein the pressure face of the first follower portion issmaller than the pressure face of the second portion.
 31. The sealingdevice as claimed in claim 29 wherein the biasing means is a spring.